1. Field
This invention is directed to a biological process for use in removing valuable metallic components from a conglomeration of other materials by biological techniques. The invention is more particularly directed to the extraction of gallium or germanium from gallium or germanium containing integrated circuits by the use of a "bioleaching" technique.
2. State of the Art
Gallium arsenide (GaAs) is used as a semiconductor in integrated circuits ("chips"). Chips containing GaAs have achieved operating speeds of up to five times that of the fastest silicon chips. The GaAs chips also operate at a wider temperature range than silicon circuits.
However gallium arsenide does have some drawbacks. Arsenic is volatile and toxic. Gallium is relatively expensive (twenty times the price of aluminum on a weight basis).
Even with the relatively high cost of GaAs chips, they have been discarded when defective or damaged. Chemically extracting GaAs from chips has been prohibitively expensive, and extraction is possibly dangerous due to the presence of arsenic.
Accordingly, it would be an improvement in the art if a relatively low cost, efficient way of extracting gallium arsenide from "rejected" or damaged chips existed.
Similarly, there has been an increased use of germanium in integrated circuitry chips, and it is clear that a process for recovering germanium from this source would also be an improvement in the art.
As reported in Lundgren et al., "Ore Leaching by Bacteria," Ann. Rev. Microbial, 34: 63-83 (1980), Thiobacillus ferrooxidans has been used to oxidize gallium sulfide (Ga.sub.2 S.sub.3) to gallium sulfate (Ga.sub.2 (SO.sub.4).sub.3). Torma, in "Oxidation of gallium sulfides by Thiobacillus ferrooxidans", Can J. Microbial, 24: 888-891 (1978), disclosed a method for biomining/bioleaching/biostabilization by bacterium involving inoculating a quantity of gallium-bearing chalcopyrite concentrate and 70 ml iron-free nutrient medium with prepared Th. ferrooxidans. The system is aerated with carbon dioxide (CO.sub.2)-containing air. Distilled water is added to compensate for evaporation, and the pH is maintained at 1.8. The temperature of the reaction is typically 35.degree. C.
The Bacterial Leaching of Metals From Ores, written by G. I. Karaivko, et al. and published in 1977, discusses the use of Thiobacillus ferrooxidans in leaching non-ferrous metals and sulfides. This article notes that Th. ferrooxidans may be used to leach rare metals such as gallium from the crystal structure of many sulfides and non-ferrous metals. The authors suggest a methodology for leaching non-ferrous metals in vats using Th. ferrooxidans. The method emphasizes the need for proper aeration, optimal mesh size of ore, pH at about 2.8, and a suggested reaction temperature of approximately room temperature (26.degree. C.).
These and other writings indicate an established study of bioleaching of iron- and sulfur-containing ores, but investigation has been done almost exclusively through the use of Thiobacillus species, particularly Th. ferrooxidans.
For example, bioleaching of copper from chalcopyrite containing ore is described in U.S. Pat. No. 4,571,387 to Bruynsteyn, et al. the contents of which are hereby incorporated by this reference. This patent discloses a process for leaching particular metals from ores using sulfide oxidizing bacteria.
The publication "Analytical Chemistry of Gallium" by Dymov and Sarostin (Ann Arbor Science Publishers, 1970) discusses the characteristics and properties of gallium, and discusses various methods of extracting gallium including electrical extraction, chromatography, and the use of organic solutions.
"Acid-Bacterial and Ferric Sulfate Leaching of Pyrite Single Crystals" by Keller, et al. (24 (Biotech. and Bioeng., 1982 pp. 83-96) discusses use of Th. ferrooxidans to leach pyrite crystals.
"Studies on the Chemoautotrophic Iron Bacterium Ferrobacillus ferrooxidans" by Silverman, et al. (1959) discusses a method for culturing chemoautotrophic bacterium such as Gallionella, Th. ferrooxidans, and F. ferrooxidans.
"Microorganisms in Reclamation of Metals" by Hutchins, et al. (40 Ann. Rev. Microbiol. 1986, pp. 311-36), describes various methods of leaching metals from ores using acidophilic iron-oxidizing bacteria. Hutchins further discusses the characteristics of many bacterial forms capable of effectuating bioleaching. Reference is made to bioleaching of Ga.sub.2 S.sub.3 by T. ferrooxidans.
"Biological Leaching: A New Method For Metal Recovery" (B.C. Research; Vancouver, B.C.) provides a general discussion of bioleaching of sulfides in industrial and commercial applications.
"Ore Leaching By Bacteria" by Lundgren, et al. (34 Ann. Rev. Microbiol. 1980, pp. 263-83) details the chemical mechanisms of bioleaching metals from insoluble minerals.
"Bacterial Leaching" by C. Brierley (CRC Critical Reviews in Microbiology, November 1978) discusses industrial applications of bioleaching, with particular emphasis on uranium and copper recovery. Details are provided regarding bacterial efficacy parameters.
"Continuous Bacterial Coal Desulfurization Employing Thiobacillus Ferrooxidans" by Myerson, et al. (26 Biotech. and Bioeng. 1984, pp. 92-99) discusses the increase in bioleaching activity with increase in surface substrate availability.
"Microbiological Mining" by C. L. Brierly (1982) discusses the role played by T. ferrooxidans in leaching copper from low-grade ore on an industrial scale.
"Wastewater Engineering: Treatment, Disposal, Reuse" (McGraw-Hill; 2nd Edition, pp. 494-497) discloses methods and apparatus for aeration of biological systems.
"Biologically Mediated Inconsistencies in Aeration Equipment Performance" by Albertson, et al. (47 Jr. W.P.C.F. No. 5, May 1975, pp. 976-988) provides an evaluation of aeration devices used in biological systems.
The Dorrco Technical Manual, Sec. 32, describes the operation of an agitator - slurry mixer.
"The Bacterial Leaching of Metals from Ores" by Karaivko, et al. (Technicopy Limited, 1977) provides a treatise on bioleaching methodologies, and makes reference to the aqueous migration of gallium in relation to pH values in bioleaching processes.